1 UNIT-7 FIBER OPTICS. FIBER OPTICS. HOLOGRAPHY. HOLOGRAPHY.

2 APPLIED PHYSICS CODE : 07A1BS05 CODE : 07A1BS05 I B.TECH I B.TECH CSE, IT, ECE & EEE CSE, IT, ECE & EEE UNIT-7: CHAPTER 1. UNIT-7: CHAPTER 1. NO. OF SLIDES :19 NO. OF SLIDES :19

3 S.No.ModuleLectureNo. PPT Slide No. 1 Introduction. Acceptance angle. Numerical aperture L Types of optical fibres L Attenuation in optical fibres L UNIT INDEX

4 Optical fibers are long, thin strands of very pure glass about the diameter of a human hair. Optical fibers are long, thin strands of very pure glass about the diameter of a human hair. They are arranged in bundles called optical cables and used to transmit light signals over long distances. They are arranged in bundles called optical cables and used to transmit light signals over long distances.light INTRODUCTION Lecture-1

5 Optical Fiber There are 3 parts in optical fiber. They are 1.Core2.Cladding. 3.Buffer coating.

6 OPTICALFIBER STRUCTURE

7 Core: - Thin glass center of the fiber where the light travels - Thin glass center of the fiber where the light travels Cladding : Outer optical material surrounding the core that reflects the light back into the core Outer optical material surrounding the core that reflects the light back into the core Buffer coating: Plastic coating that protects the fiber fom damage and moisture. Lecture-1Lecture-1

8 Acceptance angle

9 The maximum angle of incidence at the core of the optical fiber for which the rays undergo totall internal reflections and travel along the fiber is called acceptance angle. The maximum angle of incidence at the core of the optical fiber for which the rays undergo totall internal reflections and travel along the fiber is called acceptance angle. The acceptance angle is given by The acceptance angle is given by α m = Sin -1 [ (n 1 2 -n 2 2 )/n 0 ] α m = Sin -1 [ (n 1 2 -n 2 2 )/n 0 ]

10 NUMERICAL APERTURE Numerical aperture of a fiber is a measure of its light gathering capacity. Numerical aperture of a fiber is a measure of its light gathering capacity. The numerical aperture (NA) is defined as the sin of the acceptance angle. The numerical aperture (NA) is defined as the sin of the acceptance angle. (NA) = Sinα m = (n 1 2 -n 2 2 )/n 0 (NA) = Sinα m = (n 1 2 -n 2 2 )/n 0 Lecture-1Lecture-1

11 Single-mode fibers: If the core diameter is small it allows only one mode to travel through it. Then the fiber is called single mode or monomode fiber. If the core diameter is small it allows only one mode to travel through it. Then the fiber is called single mode or monomode fiber. The monomode fiber has very small core diameter less than 10micrometers. The monomode fiber has very small core diameter less than 10micrometers. They Transmit infrared laser light (wavelength = 1,300 to 1,550 nanometers ). They Transmit infrared laser light (wavelength = 1,300 to 1,550 nanometers ).laser Lecture-2

12 Multi-mode fibers If a fiber allows more number of modes, then it is called multimode fiber. If a fiber allows more number of modes, then it is called multimode fiber. It has larger core diameter than single mode fiber. It has larger core diameter than single mode fiber.

13 The relative refractive index difference is also larger than single mode fiber. The relative refractive index difference is also larger than single mode fiber. It transmits infrared light (wavelength = 850 to 1,300 nm) from light-emitting diodes (LEDs). It transmits infrared light (wavelength = 850 to 1,300 nm) from light-emitting diodes (LEDs). light-emitting diodes light-emitting diodes

14 Step index Fiber The refractive index of core is constant through out the core. The refractive index of core is constant through out the core. Different rays reach the exit end at different times. Therefore, the pulsed signal received at the exit end gets broadened. This is called intermodal dispersion. Different rays reach the exit end at different times. Therefore, the pulsed signal received at the exit end gets broadened. This is called intermodal dispersion.

15 Graded Index Fiber If the core has a non-uniform refractive index that gradually decreases from the center towards the core-cladding interface, the fiber is called graded index fiber. If the core has a non-uniform refractive index that gradually decreases from the center towards the core-cladding interface, the fiber is called graded index fiber. The light travels at different speeds in different directions. The light travels at different speeds in different directions.

16 A ray is continuously bent and travels a periodic path along the axis in the form of helical or skew rays. A ray is continuously bent and travels a periodic path along the axis in the form of helical or skew rays. There is no chance of intermodal dispersion. There is no chance of intermodal dispersion. Bandwidth is high. Bandwidth is high.

17 Plasticfibers Some optical fibers can be made from plastic. These fibers have a large core (0.04 inches or 1 mm diameter) transmit visible red light (wavelength = 650 nm) from LEDs transmit visible red light (wavelength = 650 nm) from LEDs

18 ATTENUATION Attenuation is the loss of power suffered by the optical signal as it propagates through the fiber. Attenuation is the loss of power suffered by the optical signal as it propagates through the fiber. It is also called fiber loss. It is also called fiber loss. Signal attenuation is defined as the ratio of the input optical power Pi into the fiber to the output received optical power Po from the fiber. Signal attenuation is defined as the ratio of the input optical power Pi into the fiber to the output received optical power Po from the fiber. Lecture-2Lecture-2 Lecture-3

19 The attenuation coefficient of the signal per unit length is given as The attenuation coefficient of the signal per unit length is given as α =10/L log (Pi/Po) dB/km α =10/L log (Pi/Po) dB/km The mechanisms through which attenuation takes place are The mechanisms through which attenuation takes place are 1.Absorption losses 2.Scattering losses `3.Radiation losses